A centralized processor dialoguing with one or more peripheral units is utilized, for example, in monitoring the progress of a number of telephone calls over connections established by a central office between calling and called subscribers. The data exchange in real time between the processor and any peripheral unit, however, is not without problems in view of the fact that the processor and the associated peripheral units generally differ as to operating modes and timing. Thus, the rate of data emission by the processor usually does not coincide with the rhythm in which a given peripheral unit scans the time slots assigned to it in a recurrent cycle or frame. Moreover, responses from the peripheral unit can be conveyed to the processor only when the latter is in condition to receive them.